A Mini Review on Electrospun PVDF-Metal Nanoparticle Composites for Electronic Applications

Abstract

Due to the increase in world population, the demand for energy is also increasing, Hence, researchers are now interested to explore alternative energy resources to that of conventional energy resources that can be found in ambient environment like mechanical vibration, fluid flow, radio and EM waves, heat, etc. Among this, mechanical energetic form is considered to be omnipresent form of energy which can be easily converted to useful power. Piezoelectric mechanism is the most efficient technology for converting mechanical energy to useful power output and ease of manufacturing [1]. During 19^th century, Curie et al and Lipmann proposed the concept of piezoelectricity [2]. Unlike any other mechanism, piezoelectricity does not require any additional voltage, contact with any other material and magnetic force field. Piezoelectricity is simply internal polarization of the material upon the application of stress, and this polarization creates electric field that can convert mechanical stress applied on the material to electrical energy [3]. Piezoelectricity can be seen in dielectric crystalline/semi-crystalline materials that possess dipole moment [2]. Piezoelectric materials ranging from naturally occurring crystals to synthetic materials such as Quartz, Rochelle salt, ceramics, polymers such as Nylons, PVDF, PVDF-TrFE  copolymers and metal/carbon-based nanoparticles [2,4]. Compared to other piezoelectric materials, polymers are generating lots of interest because of their low cost, flexibility and ease of processing. Currently fluoropolymers, especially PVDF is one of the most promising commercially available piezo-material used in diverse applications such as wearable sensors, nanogenerators, actuators and some micro-devices because of its excellent thermal and mechanical property, high sensitivity, good chemical resistance and biocompatibility [2,5]. PVDF exist in at least four crystalline phases (α, β, δ and γ). Among these, β-phase attributes piezoelectric behaviour to PVDF since it exhibits all-trans arrangement with non-zero net dipole moment. Hence, the increase in β-phase leads to a better piezoelectric property. Preferable β-polymorph can be obtained by various processes (annealing, mechanical poling, rolling and electrospinning) [5]. A typical one-step process that is widely utilized for preparing highly oriented nanofibers with excellent crystallinity is electrospinning method [6]. Additionally, mixing of nanoparticle on to the polymer matrix also shows efficient improvement in electrical properties. In this mini-review, we have covered the crystallinity, piezoelectric response and electrical applications of electrospun PVDF nanofiber with the addition of various metals, metal-oxide, core-shell and some hybrid nanoparticles. Acknowledgement: One of the author (A.A.P) wish to thank MHRD-SPARC, India (No. 2018-2019/P399) for the financial support. A.A.P also thank VIT for providing ‘VIT SEED GRANT’ for carrying out this research work.